Wastewater Valuing

Some products reaching wastewater flows are more easy to transform into energy, fertilisers, etc. than others. Sometimes those products - e.g. detergents - are more expensive than products difficult to treat (e.g. micropollutants). In countries lacking sanitation, the new generation wastewater treatment plants generating by-products are keys to attracting investors. Do you have products or recommendations for import or production licenses to enable wastewater treatment plants to valorise wastewater resources?